Printers

Printer types at a glance

Printers differ in how they put marks on paper, and that decides what they are good at, what they cost to run and what goes wrong with them. A help desk meets all of these types:

Laser printers

A laser printer prints with static electricity and heat. It "draws" the page as a pattern of electric charge on a rotating drum using a laser, lets toner powder stick to that pattern, rolls the toner onto the paper, and melts it in place. It is a page printer: it prepares the whole page in its memory before the paper starts moving, because the drum cannot stop halfway.

Inside a laser printer

• The imaging drum (photosensitive drum) is a cylinder with a coating that holds an electric charge in the dark and loses it where light hits it. It carries the image of the page as a pattern of charge. In many printers the drum is built into the toner cartridge; in others it is a separate imaging unit.
• Toner is a very fine powder of plastic particles and pigment (carbon for black). It is not ink: it is dry, it carries an electric charge, and it only becomes permanent when it is melted into the paper.
• The laser scanning unit sweeps a laser beam across the drum with a rotating mirror.
• The fuser (fuser assembly) is a pair of rollers — a heated roller and a pressure roller — that melts the toner and presses it into the paper fibers. That is why pages come out of a laser printer warm.
• Paper-handling parts: the pickup roller takes the top sheet from the tray, the separation pad keeps the next sheets back, and the transfer roller under the drum pulls the toner onto the paper. A duplexing assembly turns the sheet over to print both sides.

Color laser printers have four toners — cyan, magenta, yellow and black (CMYK) — each with its own drum or developing unit. Most place the four color images on an intermediate transfer belt first and then transfer them to the paper together.

Consumables and maintenance kits

Parts that wear out or run out are consumables. Printers count pages and warn when one of them nears its rated life:

• Toner cartridge: replaced when empty; rated by the number of pages it prints (its yield).
• Drum or imaging unit: where it is separate, it lasts several toner cartridges. A worn drum causes repeated marks and grayish backgrounds.
• Fuser: wears out after many thousands of pages; a worn fuser leaves toner that smudges or rubs off.
• Transfer roller or belt, pickup rollers and separation pad: wear out gradually; worn rollers cause jams and several sheets feeding at once.

Many business printers combine these parts in a maintenance kit, typically the fuser plus the rollers, to be installed when the printer's page counter reaches a set number. After installing a kit, reset the maintenance counter in the printer's menu; otherwise it keeps asking for maintenance that has already been done.

The laser imaging process

CompTIA describes the laser printing process as seven steps, and the exam expects them in this order. Steps 2 to 7 repeat continuously for every page as the drum turns.

1. Processing. The printer receives the print job and its raster image processor (RIP) converts the page description sent by the driver into a bitmap: a map of every dot on the page, stored in the printer's memory. A page too complex for the available memory produces a memory error or prints only partly.
2. Charging. The primary charge roller (in older printers a thin corona wire) gives the whole surface of the drum a uniform, strong negative charge. The drum is now "blank".
3. Exposing. The laser beam sweeps across the turning drum, line by line, and switches on wherever the page should be dark. Where the light hits, the coating loses most of its charge. The drum now carries an invisible image of the page: exposed spots with a weak charge in a field of strong negative charge.
4. Developing. The developer roller brings negatively charged toner close to the drum. Toner is repelled by the strongly charged areas and settles on the exposed, less negative spots. The invisible image becomes an image in toner.
5. Transferring. The transfer roller (or transfer corona) gives the paper a positive charge from behind. The negative toner jumps from the drum to the paper. A static eliminator then removes the charge from the paper, so it does not cling to the drum.
6. Fusing. The toner is only loose powder until the fuser melts it — at a temperature on the order of 200 °C (about 400 °F) — and presses it into the paper.
7. Cleaning. A rubber cleaning blade scrapes the toner that stayed on the drum into a waste container, and the remaining charge is removed (by an erase lamp or the charge roller), so the next rotation starts clean.

The order explains many print defects. A dirty or scratched drum puts the same mark at the same place on every page; a drum that is not cleaned or discharged properly prints a faint copy of the previous image further down the page ("ghosting"); a fuser that is not hot enough leaves toner that wipes off.

Inkjet printers

An inkjet printer prints by spraying tiny drops of liquid ink from hundreds of nozzles in a printhead. The printhead moves across the paper on a carriage driven by a belt and motor, while rollers advance the paper line by line. Combining cyan, magenta, yellow and black (CMYK) drops makes the colors; photo models add extra inks. Inkjets are cheap to buy and excellent for photos, but ink is expensive per page.

There are two ways to fire a drop:

• Thermal inkjet: a tiny heating element boils a bit of ink into a bubble, which pushes a drop out of the nozzle.
• Piezoelectric inkjet: a piezo crystal changes shape when a voltage is applied and squeezes the drop out. No heat is involved, so the printhead lasts longer and more kinds of ink can be used.

Ink comes in cartridges — some with the printhead built in, so every new cartridge brings a new head — or in refillable ink tanks with a permanent printhead. Two maintenance tasks come up again and again:

• Clogged nozzles. Ink dries in nozzles that are not used for a while, which shows up as horizontal white lines or a missing color. Print a nozzle check pattern, run the head-cleaning routine from the printer's menu or software (it uses ink), and repeat if needed. Printers that print regularly clog less.
• Calibration (alignment). After a new cartridge or printhead, lines can be jagged or colors slightly offset. The alignment routine prints a test pattern and adjusts the timing of the nozzles.

Thermal, impact and 3D printers

Thermal printers

A thermal printer uses a printhead with a row of tiny heating elements. There are two kinds:

• Direct thermal: special heat-sensitive paper turns dark where it is heated. No ink, no toner, no ribbon — only paper. This is how most receipts are printed. The print fades over time and darkens when exposed to heat or sunlight, so it is not suited for documents that must last. The paper is coated on one side only; a roll loaded the wrong way round prints blank.
• Thermal transfer: the heat melts wax or resin ink from a ribbon onto the label. The result is durable, which is why it is used for barcodes, asset tags and shipping labels that must survive handling.

Thermal printers have few moving parts and are very reliable. Maintenance is mostly replacing the paper or ribbon and cleaning the printhead with isopropyl alcohol, following the manufacturer's instructions, when prints get streaky.

Impact printers

An impact printer makes marks by physically striking an inked ribbon against the paper. The common type is the dot matrix printer: its printhead has a column of pins (9 or 24 are common) that fire individually to form characters out of dots. Impact printers are loud and slow, but they are the only printers that can print multipart forms: the force of the pins goes through to the copies below, using carbon or carbonless paper. That keeps them in use for delivery notes, invoices and logistics.

They often use continuous paper with holes along both edges, pulled by a tractor feed. Typical problems: faded print (replace the ribbon), a thin white line through every character (a broken or stuck pin), and paper that tears or drifts (misaligned tractor feed).

3D printers

A 3D printer builds a physical object layer by layer from a digital model. Software called a slicer cuts the model into thin layers and creates the instructions for the printer. Two technologies are common:

• Fused deposition modeling (FDM): a heated nozzle melts plastic filament from a spool and draws each layer onto a build plate. Filaments such as polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) are common. Typical problems are a clogged nozzle, prints that do not stick to the plate, and a plate that is not level.
• Resin printing (stereolithography, SLA, and related methods): ultraviolet (UV) light hardens a liquid resin layer by layer. The detail is much finer, but liquid resin irritates the skin, so it is handled with gloves in a ventilated space.

Connecting and sharing printers

A printer can reach its users in several ways:

• Universal Serial Bus (USB): directly to one computer. Simple, but only that computer can print, unless it shares the printer.
• Wired network (Ethernet): the printer has its own Internet Protocol (IP) address and anyone on the network can print to it. Give it a fixed address — a static address or a Dynamic Host Configuration Protocol (DHCP) reservation (see DHCP) — because computers that print to an IP address lose the printer when its address changes. That is a classic cause of "the printer is offline".
• Wireless: joined to the Wi-Fi network like any other client, or offering a direct connection of its own (often called Wi-Fi Direct) for devices without network access.
• Shared through a computer or print server: the operating system (OS) shares a locally connected printer, or — in organizations — a print server holds the queues and drivers for many printers centrally. Users connect to the server, which hands out the right driver automatically.

The print queue and the spooler

A computer does not send a document straight to the printer. The print spooler — a background service — stores each job on disk in a print queue and feeds jobs to the printer one at a time, so the application can carry on while the printer works. When one job gets stuck, every job behind it waits. The fix is to cancel the stuck job and, if the queue will not clear, restart the spooler service (on Windows it is called Print Spooler; restarting it needs administrator rights). Illustrative PowerShell:

Get-PrintJob -PrinterName "Office-Laser-2F"

Id    ComputerName    PrinterName        DocumentName        SubmittedTime          JobStatus
--    ------------    -----------        ------------        -------------          ---------
14                    Office-Laser-2F    Q3-report.pdf       9/28/2026 9:14:03 AM   Error, Printing
15                    Office-Laser-2F    Invoice-0415.docx   9/28/2026 9:15:40 AM   Normal
16                    Office-Laser-2F    Timesheet.xlsx      9/28/2026 9:21:12 AM   Normal

Remove-PrintJob -PrinterName "Office-Laser-2F" -ID 14
Restart-Service -Name Spooler

Drivers and page description languages

The printer driver translates what the application wants to print into a language the printer understands, a page description language (PDL). The two classic ones:

• Printer Command Language (PCL), originally from HP and now supported by most office laser printers. Fast and compact, and the usual choice for everyday office printing.
• PostScript, originally from Adobe: a device-independent language that describes the page precisely, so it prints the same on every PostScript printer. Common in graphic design and publishing.

Many printer models come with both a PCL and a PostScript driver. Manufacturers also offer universal drivers that work with a whole range of their models, which simplifies print servers. At the time of writing, operating systems increasingly print without a model-specific driver, over the Internet Printing Protocol (IPP) with a generic class driver ("driverless" printing). When the driver and the printer disagree about the language, the printer prints what it receives literally: pages of random characters and symbols.

Printer settings and security

Settings users ask about are mostly in the driver's preferences or the printer's own web interface: duplex (both sides), orientation, paper tray and size (A4 in Europe and the UK, Letter in the US and Canada; the document and the tray must agree), and print quality or toner-saving mode. Network printers are also computers on the network, so treat them that way: change the default administrator password, install firmware updates, and consider features such as secure print or badge release, where a job only prints after the user authenticates at the printer, so confidential pages do not lie in the output tray.

Consumables and cost per page

The purchase price of a printer says little about what it costs. What matters over its life is the cost per page: the price of a cartridge divided by its yield, the number of pages it prints. Manufacturers measure yield with standardized test pages from the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) — ISO/IEC 19752 for monochrome toner, ISO/IEC 24711 for inkjet — that cover only a small part of the page, so a user who prints dense pages gets fewer. The numbers below are made up for the example; the calculation is what counts:

# Example numbers only: prices in an imaginary currency, yields as rated by the maker
cartridges = [
    ("Inkjet, standard black", 20.00, 400),
    ("Inkjet, high-yield black", 32.00, 1_000),
    ("Laser, black toner", 80.00, 3_000),
]
RATED_COVERAGE = 5        # percent of the page covered by toner or ink in the yield test
pages_per_month = 1_500

for name, price, rated_yield in cartridges:
    per_page = price / rated_yield
    print(f"{name:<25} {per_page:.3f} per page, {per_page * pages_per_month:6.2f} per month")

# Dense pages use more: at 15% coverage a cartridge lasts about a third as long
coverage = 15
name, price, rated_yield = cartridges[2]
real_yield = rated_yield * RATED_COVERAGE / coverage
print(f"{name} at {coverage}% coverage: about {real_yield:.0f} pages, "
      f"{price / real_yield:.3f} per page")

Inkjet, standard black    0.050 per page,  75.00 per month
Inkjet, high-yield black  0.032 per page,  48.00 per month
Laser, black toner        0.027 per page,  40.00 per month
Laser, black toner at 15% coverage: about 1000 pages, 0.080 per page

Two lessons for recommending a printer: the most expensive cartridge can be the cheapest per page, and the difference grows with volume. A full cost comparison also counts the drum, fuser and maintenance kits for lasers, and the ink used by head cleaning for inkjets.

Common problems and fixes

Most printer tickets fall into a small number of patterns. The symptom usually tells you which part of the process failed:

Safety

Printers are among the few devices at the help desk that can burn you. The general rules are on Safety and Handling; for printers specifically:

• The fuser is hot. Turn the printer off and let it cool before you reach in to clear a jam near the fuser or replace it; most printers carry a warning label at that spot.
• Toner is a fine powder. Do not breathe it in and do not use an ordinary vacuum cleaner on spilled toner: the particles pass through normal filters and can be a fire hazard in the motor. Use a vacuum made for toner. Wash toner off skin and clothing with cold water — warm water can melt it into the fabric.
• High voltage and lasers. The charging parts and the power supply work with high voltages, and the laser can damage eyes. Replace whole modules; do not open the laser unit or the power supply.